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BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
UNIT I
Pc Hardware Overview
Introduction – Basic Parts of PC – Functional block diagram – system board – Microprocessor –
Interrupts – DMA – SMPS – BIOS – POST sequence - System configuration – Memory – Mass
storage – I/O interface standards
1.1 INTRODUCTION
A personal computer (PC) is comprised of hardware, an operating system and software. Each
of those components is fairly complex, however this article provides a basic description of
their function and how they work together.
The Hardware
The most fundamental elements of a PC's hardware are the Central Processing Unit (CPU)
and memory modules mounted onto a motherboard. When the PC is powered on, the CPU
begins communicating with the motherboard and starts the Basic Input Output System
(BIOS) which is stored on a chip on the motherboard. After verifying that the required
components are present and functioning, it searches for an Operating System (OS). It may
check the floppy drive, hard disk or CD-ROM for the presence of an OS.
Other common examples of hardware which may be a part of a PC include a modem, sound
card, network card, and video card. The components attached outside of your computer such
as the keyboard, mouse, printer and monitor are called peripherals.
For more information about each of the hardware components of a PC, see our article "The
Parts of a Personal Computer". For more technical information about how the hardware
works, refer to our articles for specific Hardware Info.
The Operating System
The OS is responsible for everything from enabling hardware components to function
(components like modems, printers and monitors) to how to communicate with the Internet as
well as playing the role of traffic cop for all of the software.
The OS allocates the resources of the PC to the software and hardware in an organized way.
The resources include things like memory storage space, access to the hard disk and what is
displayed on the monitor. Without the OS, the software programs might interfere with each
other, causing the PC to malfunction or crash continually. Even with the OS, many PCs have
difficulty operating smoothly. That illustrates just how complicated the tasks of an OS
actually are.
The Software
While the OS is technically a software program, it is distinct from other software specifically
referred to as "application software". Application software, we'll just call it software, are
programs that you install onto a PC that make the PC useful.
Software is a complex series of instructions telling the computer what to do. The instructions
are very detailed because they have to tell the computer every single step to be performed.
For example a word processing program has instructions for what to do when you press the
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
letter "A". The software tells the computer to take the letters as they are pressed on the
keyboard, then it tells it to add the letter to the letters you already typed and it tells the
computer to display the letter on the screen so you can see what you have typed. The
computer doesn't do anything without very explicit instructions.
1.2 Parts of a Personal Computer
A personal computer is made up of many components; called "hardware". A typical PC
contains the following hardware:













Case
Power Supply
Motherboard
CPU
Memory
Hard Disk
Floppy Disk
CD-ROM
Video Adapter
Sound Card
Modem
Mouse
Keyboard
.There are many other possible hardware components, such as a DVD, CD-RW, Zip drive or
network card. There are also many subcomponents of a PC, such as the cooling fan, printer
port or reset switch to name a few. The hardware in the list above is nearly universal to a
basic PC.
While a PC is built up from hardware components, the hardware is only half of the equation.
The other vital part of a PC is the software. Without software, the hardware is useless; and
vice versa.
The fundamental software for a PC is called an "operating system". Without an operating
system or "OS", a PC can't do much. The operating system tells the components of a PC what
to do and when to do it. Windows, MAC OS, Linux and Unix are all examples of operating
The Case
The case is the box that houses the PC. All of the hardware, except for the peripherals, is
housed inside the case. There are two common styles of cases: "desktop" and "tower." The
desktop case usually sits under the monitor and is roughly the size of two or three shoe boxes
side by side. The tower case stands upright on one end and is usually placed on the floor.
Tower cases can be the same size as a desktop case but often range up much larger. Another,
less common, case style is the "rack mount" case which slides in and out of an equipment
rack.
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
The Power Supply
Where the power cord connects to the back of the PC is the power supply. The power supply
converts AC current from the wall outlet to the appropriate DC voltages for the various
components of the computer.
The power supply has a fan built into it to keep itself and the PC cool. Most PC's have at least
one additional cooling fan, often mounted directly on the CPU. The power supply or its
internal fan can wear out. Fortunately, the entire unit is easily replaced.
The Motherboard
The motherboard is the largest and most fundamental component of a PC. Every other
hardware component is somehow attached to the motherboard. The motherboard is the
common link for every component to communicate and work together.
The motherboard has a series of slots, sockets and connectors for connecting the various
components of a PC. The memory, accessory cards, and CPU are installed directly onto the
motherboard in most cases. The drives and peripherals communicate with the motherboard
through wired connections.
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
It is becoming increasingly common for motherboards to integrate features that used to
require separate accessory cards. Most motherboards integrate drive controllers and
communication ports; and with greater frequency they integrate sound, video and network
features as well.
There are a wide range of motherboards to choose from. They differ in features, speed,
capacity and the CPU supported. They also differ in size, shape and layout, this is commonly
referred to as the "form factor".
The CPU
The CPU, which stands for Central Processing Unit, is the brain of the PC. It is often referred
to as the "processor" or "chip". The CPU directs, coordinates and communicates with the
hardware components and performs all of the "thinking". What a CPU actually does is
perform mathematical calculations. It is the software that people write that translates those
calculations into useful functions for us.
The speed of the CPU, generally speaking, is the number of calculations it can perform in one
second. It is more complicated than that, but it is a reasonable way to think of the speed. A
500 MHz (megahertz) CPU performs about 500,000,000 mathematical calculations per
second.
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
As the speed of new CPUs increase, the difference is becoming less obvious to computer
users. A CPU that is twice as fast as another one will not result in a PC running twice as fast.
The CPU has to wait for other, slower components and for the user too. The CPU spends a lot
of time sitting idle, waiting for something to do.
CPUs have something called a "cache" or memory cache. The memory cache is where
information is stored that the CPU is likely to need soon. This memory is in addition to the
normal memory installed in a PC. The difference is that the cache is built right onto the CPU
(and/or very near the CPU), and it is much faster than conventional memory. Cache memory
was developed to reduce the time the CPU had to wait while information was retrieved from
the standard memory.
The RAM Memory
The memory chips store information, temporarily, for short term use. A PC's memory is an
entirely different thing from the hard disk "memory". The hard disk stores information
"permanently" for long term use.
A PC's memory only contains information when the PC is on. When the PC is turned off, the
information in the memory chips disappears. The information in memory is similar to a
thought, it gets replaced when you start thinking about something else. Hard disk memory is
like writing down the information and storing it in a filing cabinet.
The Hard Disk Drive
A hard disk (also called a "hard drive") is much like a filing cabinet. The programs and data
are stored on the hard disk and the computer accesses them as needed. When the computer
accesses the hard drive, it is reading the stored information into memory. That memory is the
temporary workspace. The original file on the hard disk is left undisturbed. When the
computer stores information, it writes the data to the hard disk. That process results in the old
file being replaced or modified with the new information. If you save data to a new file, or
install new software, the information is written to the disk in an available, unused portion of
the disk.
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
The Floppy Disk Drive
The floppy disk drive is a device that records data onto a removable storage disk called a
floppy disk. Floppy disks, also called "floppies", are the most basic storage medium for data.
However their limited capacity, typically 1.44 megabytes, makes them of limited use.
A floppy disk can be used to copy files from one PC to another PC or for making backup
copies of files. Replacing a floppy drive is very easy and inexpensive to do, should the need
arise.
The CD-ROM
The CD-ROM drive is a device that reads information or music off of a compact disk (CD).
CD-ROM stands for Compact Disc Read Only Memory. Most software is distributed on CDs
because of their low cost and large capacity (650MB or more).
The CD is spun at high speed inside the drive while a laser is directed at the surface to read
the data or music. The CD-ROM speed is referenced as 12X or 12 speed (or any other
number). This simply means that it spins the CD that many times faster than the original
industry specification. So, a 48X CD-ROM spins the CD up to 48 times faster than the
original specification. Faster is better.
Many PCs are now built with a CD-RW drive, which stands for Compact Disc, Read-Write.
Unlike a standard CD-ROM, you can write data onto a CD with a CD-RW drive. CD-R disks
allow you to write to the CD once and read it an unlimited number of times. With the use of
RE-writable CDs (CD-RWs) you can reuse the disk and rewrite over it again many times.
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
The speeds of a CD-RW are expressed like this, 4X 4X 32X. This means it can write to the
CD up to 4 times the spec speed, rewrite the CD up to 4 times spec speed and read the CD up
to 32 times the spec speed.
The Graphics Card or Video Card
The video adapter card or graphics adapter translates information into graphics and text that
appear on the monitor screen.
The graphics adapter plugs into a slot on the motherboard or is incorporated directly into the
electronics of the motherboard. Most motherboards now include a slot specifically designed
for the graphics adapter called the AGP slot (Advanced Graphics Port).
Modern graphics adapters usually incorporate some memory right on the card to improve
their performance. To further improve the performance of the video output, a second graphics
accelerator card can be used in tandem with the graphics adapter.
The Sound Card
Most PCs are typically equipped for multimedia. They can play sounds, music, and speech.
The sound card processes the information and outputs the signal to the speakers.
The sound card plugs into a slot on the motherboard or is incorporated directly into the the
motherboard. With a basic sound card a microphone, speakers, joystick and an auxiliary
sound source can be connected to it. More advanced cards may offer additional input and
output features.
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
The Modem
The modem is a device that enables the PC to use a telephone line to communicate with other
PCs and devices. The name comes from "MOdulation DEModulation".
The modem plugs into a slot on the motherboard or is incorporated directly into the
electronics of the motherboard. It converts data into signals that can be transmitted over the
telephone line and receives data to convert back for the PC to use.
The Mouse
The mouse is a user input device that enables you to communicate with your PC. By moving
the mouse and pressing the two or three buttons, you can highlight and select images on the
screen to give directions to your PC. Some mice offer a wheel to aid in the scrolling of a
window without having to move the mouse.
A mouse is usually connected by a wire but wireless mice are also available. Wired mice may
use a serial, PS/2 or a USB port. Other variations of mice available include the trackball and
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
touchpad.The mouse detects movement either as a ball underneath the mouse rolls along your
desk or by using a light inside the mouse and measuring the reflection from the desktop.
The Keyboard
The keyboard is the primary user input device. It enables you to communicate with your
computer. While the mouse is also a fundamental device to control the PC, the keyboard goes
one step further by allowing you to enter specific information as opposed to simply pointing
and clicking.
The keyboard connects to the computer through a wire, although wireless keyboards are also
available. Variations of the classic keyboard include the addition of action specific buttons,
most commonly for Internet features, and split keyboards which angle the two halves of the
keyboard to reduce stress on your wrists as you type.
2.Functional Block diagram of a PC:
Personal computer is a computer used for computational purposes. It has many components
to perform the operations. This can be represented by means of a block diagram which
explains the functionality of a PC.
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

The blocks inside the system box are called as internal units.
The blocks outside the system are called as external units.
The expansion box provides additional memory.
The external units are connected to the system box by separate cable.
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BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
CRT Monitor
Expansion box
System box
Printer
Keyboard

Switch Mode Power Supply (SMPS) provides different voltage levels as +5V,
-5V to all the internal units.
CPU:
ALU is a 10 bit register which provides the high speed processing power.
 ROM is a basic IO system used to store the system program.
 RAM is used to store the application program.
+5 V
GND
Control bus
Clock 1
reset
Ready
8088
Address / data bus
Interrupt
NMI
Multiplexed 20 bit
bus
Fig., pin details of 8088 microprocessor




Floppy disk is controlled by floppy disk controller which communicates with
DMA, CPU and the memory.
Hard disk id controlled by the hard disk controller which communicates with
DMA, CPU and the memory.
20-bit address bus and 8 bit data bus.
Printer is controlled by key printer controller.
2. MOTHERBOARD LOGIC:
Motherboard logic is a microcomputer with add-on peripheral interface controller.
 Keyboard interface is a part of motherboard logic.
 Other interface controllers are mounted as separate board on the motherboard.
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1








When the power is ON, the microprocessor reads the data from the ROM.
After the post sequence is over, boot program from FDD and HDD are stored in
RAM.
There are one or more ROM chips on the motherboard.
The ROM chips in the PC are byte organized.
The location of each ROM contains 8 bits.
The RAM chip in the PC are bit organized.
The location of each Ram contains one bit.
9th bit is used as the parity bit.
2.1 Reset logic:
It is the part of motherboard logic.
 The use of SMPS is to operate different DC voltage levels in the range of +5V,
+12 V, -5 V, -12V.
 The power good signal ensures that the dc voltages are good and it can be used.
 The power good signal is generated by SMPS with some delay.
 At that time, the system remains in reset condition.
 If the system is working, the power good signal is removed by the SMPS by the
following conditions.
1) The range of AC input is beyond SMPS range.
2) Bad DC output.
2.2 Keyboard interrupts:
 Keyboard interface is also a part of motherboard logic.
 Keyboard interface receive the keyboard serial data, it should be converted into
parallel data.
2.3 Interrupt logic:
 It receives several interrupt from interrupt sources.
 Interrupt logic send an input to the CPU.
 CPU acknowledges the interrupt to the interrupt logic
 Interrupt logic send vector code to the CPU.
 CPU used with a code and branch this into interrupt subroutine.
2.4 Ram parity logic:
 It is a part of motherboard logic; this logic contains odd parity generator and odd
parity checker.
 Odd parity generator is used to generate the parity bit or extra bit into the original
data/user data written into the RAM.
 Odd parity checker checks the number of one’s whether it is even or not. If it is
odd means ‘no error’ and if it is even means ‘error’.
2.5 NMI logic:
NMI logic produces NMI signal to the CPU by the following conditions:
 Ram parity error on the motherboard.
 Co-processor error.
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BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
2.6 Memory refreshes logic:
It generates the refresh indication to the RAM logic every 50 microsecond.
2.7 WAIT STATE logic:
It generates the wait state to the CPU or DMA to synchronize with the CPU or DMA
controller with the memory or IO ports.
2.8 Bus arbitration logic:
 Provides service for DMA controller.
 It generates the wait state to the CPU.

2.9 Ram logic:
 Ram logic is used to interface the Ram chips into the address and control signal.
 Ram logic is used to select Ram bank with the location.
2.10 ROM logic:
 It is used to select ROM bank with the location.
Fig., RAM logic
2.11 CPU logic:
 It contains the microprocessor and the subroutine chips.
 It provides address, control&data bus.
Fig., CPU Logic

It generates the signal from WSL and BAL.
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BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1

It generates the INTR and NMI signal.
2.12 DMA logic:
 Used for data transfer between the memory and IO controller.
 It receives the request from floppy disk controller and hard disk controller.
FIG., DMA Logic
4.Motherboard:
The motherboard is the most important part of the computer.Although there are a
number of components that a PC cannot function without its motherboard which ties them all
together to two them in to personal computer.
The motherboard of PC is a large printed circuit board that is home to many of the
most essential parts of the computer,including the microprocessor,chipset,cache,memory
sockets,expansion bus,parallel and serial ports and keyboard connectors and IDE,EIDE or
SCSi controllers among other components of the PC.
Motherboard Designs:
i)The motherboard Style (integrated style)
ii)The backplane Style(non-integrated style)
The motherboard style:
A motherboard aggregates all of the PC’s primary system components on a single
printed circuit board (PCB).In motherboard’s single board design all the PC’s electronic
circuitry that provides the conduct through which all operations flow is located on the
motherboard.
Backplane style:
Backplane style mainboards are less popular today than they were in the mid-to late of
1980’s but still around.
Backplane mainboards are commonly in large pc network servers and on other
computers on which the processor is upgraded frequently.
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BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
Types of backplane :
1.Active backplane 2. Passive backplane
Passive backplane:
A backplane mainboard contains very little in the way of intelligence and storage
capabilities.It is merely a receptable board into which processor cards,memory cards and the
other components are inserted to add capability to a PC.
Active backplane:
This mainboard design is also referred to as an intelligent backplane because it adds
capability to the main backplane board to help speed up processing.Actually this type of
motherboard have slot1 or slot2 sockets for Pentium II and Pentium III xeon .
Motherboard form factors:
A form factor defines a motherboard’s size shape and how it is mounted to the case,the
type,placement and size of the power supply,the system’s power requirements,the location
and type of external connectors and the case’s airflow and cooling system.
The table list the more common PC form factors used in PC’s.
Form factor
IBM PC
IBM PC XT
LPX
Mini LPX
Width(in
inches)
8.5
8.5
9
8-9
Length (in
inches)
13
13
1113
10-11
Design type
Case type
Motherboard
Motherboard
Backplane
Backplane
IBM PC
IBM PC XT
Low profile
Low profile
The components of the Motherboard:
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Prepared by Mrs.M.Buvanesvari (AP/IT/RGCET)
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
EXPANSION SLOT
I/O CONNECTOR
POWER
CONNECTOR
MEMORY SOCKETS
CHIP SET
CPU SOCKET
CMOS
BATTERY
The major parts of the motherboard are:
CPU slot and socket :
The CPU mounts to the motherboard through either a slot or socket mounting.
Chipset:
Many of the circuit and CPU level functions are contained on the chipset.
Memory Sockets:
Depending on the age of the PC, its memory is mounted on the motherboard as
individual memory chips that fit into separate (DIP)-dual inline packaging sockets or memory
module.
BIOS ROM:
The BIOS is stored as firmware on a read only memory chip.The BIOS is used to start
the PC up when the power is termed on and provides a link for the CPU to the PC’s
peripheral devices.
CMOS Battery:
The configuration of a PC at the systems level is stored in a type of memory,CMOS
(complementary Metal oxide semiconductor) that requires very little power to hold its
contents.The CMOS battery supplies a steady power source to store the system configuration
for use during the PC’s boot sequence.
Power Connector:
A connection must be made to the power supply so that power is available to the
circuitry on the motherboard.Motherboards use different voltages of power for different
components on the board.
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BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
I/O Connector:
The motherboard includes a variety of external I/O connectors that allow external
devices to communicate with the CPU.
Expansion Slots:
External peripherals and internal devices are interconnected into the motherboard and
cpu through the expansion bus.The motherboard features a variety of expansion slots that
usually include three or more of the different expansion buses available.
MICROPROCESSOR
 A microprocessor is a multi function IC in essence of the computer.
 Integrated circuit – combination of electronic components such as transistors,
capacitors, resistors.
 CPU – called as Processor has several parts.
 Parts:
i.
Control Unit (CU)
ii.
Protection Test Unit (PTU)
iii.
Arithmetic & Logic Unit (ALU)
iv.
Floating Point Unit
v.
Memory management Unit
vi.
BIU
vii.
PFU
Decode unit, Registers, CPU Bus System, Sockets & Slots.
CU: Controls the function of CPU.
Eg: Kind of manager who co-ordinates the activities between different levels of factory.
CU tells other parts of the CPU
i.
How to operate
ii.
What data to use.
iii.
Where to put results.
PTU: It works with CU to monitor whether the unit works properly (or) correctly.
If it detects something is not done properly, it generates error signal.
ALU: Performs all calculations & comparative logic functions for the CPU, including +, -, *,
/, =, >=, <=, etc...
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BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
FPU: Other names including
i.
Math Co-Processor
ii.
Numerical Processing Unit. (NPU)
iii.
Numerical Data Processor. (NDP)
 Handles all floating point operations for the ALU and CU.
 Floating point operations arithmetic on numbers with decimal places.
 Math operations include trigonometry, logarithms.
 Acts as a catalogue. Helps for fast processing.
MMU:
 Handles addressing & cataloging of where data is stored in system memory.
 Whenever CPU needs something from memory, it requests it from the MMU.
 MMU manages memory segmentation & paging allocates & translates all logical
addressing into physical addressing.
BIU: Transfer of data’s over the bus system. Transfer data from one to another.

Used to check whether data properly transferred or not.

Serves as interface point for the CPU and its external bus.
PFU:
 Pre-loads the instruction registers of CPU with instruction from memeory.
 PFU does not analyze instructions
 Gets the next instructions
 Decode Unit : It decode incoming instructions.
 PFU retrieves more instructions & this decode unit, decodes then to get them ready
for the control unit.
REGISTERS:
Storing the data’s & instructions

Built into the CPU.
CU
PTU
BIU
ALU
FPU
MMU
PFU
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REGISTERS
BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1

Buffers that are used to temporarily hold the data, addresses, instructions being
passed around between these CPU’s components.
CPU’s Bus System:

Bus-pathway carries various signals, addresses & data.

Bus structures have different sizes, ranging from 16 to 64 bits on modern
microprocessor & their size determines the amount of data to be transmitted.

64-bit bus carriers more data than a 16 bit bus.
i.
Data Bus: Carries Information to & from the CPU.
ii.
Address Bus: Carries the address from where data is to be read, to where data is
to be written.
iii.
Control Bus: Caries the signals used by the CPU.
(a). When data is ready to be read.
(b). When another device wishes to use the bus.
(c). Type of operation to be performed.
TERMS USED IN MICROPROCESSOR LITERATURE:
Bit → A digit of the binary number (or) code is called bit.
Nibble → The 4 bit binary number or code.
Byte → The 8 bit binary number or code.
Data → The quantity ( binary number or code) operated by an instruction of a program is
called data.
The size of the data is specified as bit, byte, word,etc.
Word → The 16 bit binary number or code.
Microprocessor:
 It is a programmable controlled device which fetches (from memory), decodes &
executes instructions. It is used as CPU in computers. Most Microprocessors are
single chip devices.
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BRANCH:IT THIRD YEAR /FIFTH SEM
SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
 The 8085 processor has 8 bit ALU, hence called as 8-bit microprocessor.
 The 8086 processor has 16-bit ALU, hence it is called 16-bit processor.
 Bus: A Bus is a group of conducting lines that carries data, address & control signals.
i.
Data Bus (Group of connecting lines that carries data)
ii.
Address Bus (Group of connecting lines that carries address)
iii.
Control Bus. (Group of connecting lines that carries control signals
CPU Bus: The group of conducting lines that are directly connected to Microprocessor is
called CPU bus.
In CPU bus, the signals are multiplexed i.e. more than 1 signal passed through same line but
at different timings.
System Bus: The group of conducting line that carries data addresses & control signals. In
system Bus, multiplexing is not allowed.
Advantages of Microprocessor based system:
1. Computational / processing speed is high.
2. Intelligence has been brought to systems.
3. Automation of industrial processes & office administration.
4. Less number of components, compact in size, cost less. Also more reliable.
5. Operation & maintenance easier.
Disadvantages of Microprocessor based system:
1. It has limitations on the size of the data.
2. Most of the microprocessor does not support floating point operations.
3. Speed & execution – slow & so real time applications are not possible.
INTERRUPTS:
An interrupt is a signal from a device attached to a computer or from a program within the
computer that causes the main program that operates the computer (the operating system ) to
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stop and figure out what to do next. Almost all personal (or larger) computers today are
interrupt-driven - that is, they start down the list of computer instruction s in one program
(perhaps an application such as a word processor) and keep running the instructions until
either (A) they can't go any further or (B) an interrupt signal is sensed. After the interrupt
signal is sensed, the computer either resumes running the program it was running or begins
running another program.
 The CPU supports one level of non- maskable interrupt and 8 levels of maskable
interrupts.

The NMI (non maskable interrupt) is created for any of the 3 conditions
1. RAM parity error on the motherboard.
2. Parity error in the daughter board.(expansion board)
3. Co-processor error.
NMI logic

The NMI cannot be ignored or masked, but there is a hardware overwriting facility to
block there NMI under software control.
 This is exercised by the software usually immediately after power ON. The 8088 µp
supports only one interrupt I/P for maskable interrupts. With the addition of the
interrupt controller assigns parity bits among the 8 interrupt requests.
 The interrupt controller senses the presence of interrupt request and sends an interrupt
signal (INTR) to the 8088.
 The 8088 then interrogates the interrupt controller supplies the vector code,
corresponding to the interrupt level which has the highest priority among the
interrupt levels active.
 Using the vector code, the 8088 branches to the corresponding interrupt service
routine.
 Any of the interrupt levels can be masked by the software
 The interrupt controller ignores interrupt request from those level which are masked.
LEVEL
SIGNAL
SOURCE
REMARKS
Generated at the rate of 18.2
cycles/sec used to update and
0
IRQ0
Timer 0
maintain date and time by
software
On receiving a scan code from the
keyboard, the keyboard interface
Keyboard
generates IRQ1 for every key
1
IRQ1
interface
typed; the keyboard sends two ”
scan code” (a) make (b) break
hence 2 interrupts for each key.
Not used in common PC’S used
2
IRQ2
for additional peripheral
systems(eg. scanner)
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3
IRQ3
Special port
(secondary)
4
IRQ4
Special port
(primary)
5
IRQ5
Hard disk
controller
6
IRQ6
Floppy disk
controller
7
IRQ7
Parallel port
Generated by the second set of
serial(asynchronous or
synchronous for every byte of
data to be transferred used also
for error condition).
Generated by the first set of serial
port
Generated at the end of data
transfer operation or completion
of a command by the HDC
Generated at the end of data
transfer operations or completion
of a command by the FDC.
Transferred on every byte of data
transferred.
1. KBI – keyboard interrupt is used for data transfer ie transfer the seen code for the by
pressed to the CPU.
2. SPI- serial port interrupt from floppy disk controller provides status information. It
usually occurs during i/o completion stage.
3. FDC- the interrupt from hard disk controller is similar to the at of FDC
4. HDC- The interrupt from hard disk controller is similar to that of FDC
5. Timer interrupt – it indicates the underflow of the down counter in the timer. The
down counter counter is used for the purpose of a real time clock. The real time clock
is provided by the combination of timer & the software.

The printer adaptor or printer interface provides 2 options
1. Interrupt mode & DMA mode
2. Programmed mode for data transfer.

The FDC uses the DMA mode command provide transferred using the
programmed mode.
6. SWITCH MODE POWER SUPPLY

Used to provide different DC voltages.

The power supply used in computer is SMPS.

Most of the electronic circuits need low power at different voltage levels.
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
The power from the main is 220V and 50Hz.

This should be converted into low voltage DC by step down transformer, rectifier and
filter.

Rectifier and filter is used to convert the AC input power into high volt DC. This is
first stage in block diagram.

High frequency switch converts high volt DC into high frequency AC.

The output of the switch is given to the primary side of transformer.

The output of secondary step down transformer is low volt AC.

The last stage of the rectifier and filter is used to convert low volt AC to DC which is
the output.

Most of the switching power supply uses pulse width modulation.

The sample output is sent to the high frequency switch to control the level of the
output voltage.
Fig,. SMPS block diagram
There are two types of SMPS namely
1. AT power supply
2. ATX power supply
1. AT power supply:

PC needs two different voltage level such as +5v, -5v, +12v, -12v.

Most of the electronic circuits require +5v DC.

+12v is used to operate disk drive motors.
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
-5v is used for dynamic memory bias voltage.

-12v is used for RS 232C serial interface.

The supply is given to the SMPS box by two 6 wire connector and 4 wire connector,
labeled as P8, P9, P10 and P11 respectively.

Power signal is used fro CPU processing.
2. ATX power supply:


This is second model of SMPS.
It is a 20 pin connector with square hole for 1st pin and round hole for remaining 19
pins.

There is ATX auxiliary connector (6 pins) and optional connector (2x3 pins
connector)
Signals used in ATX connector:
i.
3.3v: used to support the low voltage logic in computer.
ii.
+5v: used to send the power to all the components like floppy disk, hard disk and
compact disk.
iii.
Gnd: provides ground connection to all the devices.
iv.
+12v: used to operate the disk drive motor.
v.
-5v: used to operate dynamic memory bias voltage.
vi.
-12v: used for RS 232C serial interface.
vii.
Power good: tied to the CPU reset pin .if the power of PC is ON, then switch
logic is 1. CPU is continued in reset mode, then the power is stable, here switch
logic is 0. The CPU can begin processing.
viii.
Power on: it is a low active signal. It’s used to turn on the main power output of
+5v, -5v, +12v & -12v. If the signal is high, the main power output should be
OFF.
ix.
+5v stand by: is used in power circuits. It needs power during power down. It
supplies the +5v Dc with minimum of 10mA.
x.
Power OK: it is a power good signal is set to be logic ‘1’ by power supply that
indicates the +5v and 3.3v is greater than the under voltage level.
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xi.
Fan M: this signal allows the system tom monitor the power supply for fan speed.
xii.
Fan C: this signal is used for fan speed and shut down control signals. The fan
speed and shut down is controlled by voltage deliver on the pin. The power
delivered from the pin is +12v DC for fan speed.
xiii.
3.3 v sense line: this signal is used in ATX optional connector. It is used to
control the 3.3v line at the motherboard.
xiv.
1.394 R: the voltage from the pin is used for 1.394R connectors.
xv.
1.394V: It provides the ground connection for 1.394V connections.
SYSTEM CONFIGURATION

BIOS display a summary of PC’s configuration from the CMOS.
1. PROCESSOR:

The microprocessor such as Pentium, Pentium II, Athlon, etc used in PC.

Newer version – INTEL, AJRIX, AMD processors.

Those processors – incorporate – SMM(System Management Mode),
PMS(Power Management Standard) listed as PENTIUM – S processors.
2. CO-PROCESSOR:

Separate math co-processor of FPU is integrated into the processor chip.

Then, it is found to be inside the system[CPU] & co-processor is integrated (or)
installed.
3. CLOCK SPEED:

Clock speed of the processor – MHz. [How many cycles per second the
processor runs].
4. FLOPPY DISK DRIVES:
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
Size is 3.5 inch (or) 5.25 inch.

The capacity in KB (or) MB displayed and they do not vary.
5. HDD & CD-ROM’s:
HDD:

The HDD is detected whether it is a primary (or) secondary master (or) slave.

The name of the manufacturer, the drives capacity – C,D,E,etc…
CD-ROM’s:

CD-ROM’s –connected (or) interfaced separate adapter board (or) supported by
a sound board – through - CD-ROM controller ports.
6. MEMORY SIZE:

System memory is divided into Base, Extended & Cache.

Base memory always 640 KB

Extended memory represents the remaining amount of memory on the system.

The amount of cache memory is displayed as a separate memeory.
7. MEMORY TYPE:

Do not confuse with base, extended (or) cache types.

Regarding the system memory.

Includes the number and technology of memory banks (or) modules installed on
the system. Eg: EDO DRAM at bank 1
8. VIDEO TYPE:

BIOS – Display – Video Type

VGA/CGA/MGA (Video/Color/Monochrome) – Information’s will be there
9. SERIAL PORTS:

System Resources includes IRQ & I/O port address.

These resources assigned to serial ports by BIOS.
10. PARALLEL PORT:
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
IRQ, I/O port address – assigned system resources.

Parallel ports – displayed by the BIOS.
11. PLUG & PLAY DEVICES:

Plug & Play adapter cards information’s- displayed by bios.
12. MEMORY:

Stores data (or) instructions on your PC-Memory.

PC’s memory – made up of – Electronic components.

Memory are
i.
H.D
ii.
F.D
iii.
ROM, RAM
iv.
Cache
v.
CMOS (Non-volatile RAM. It cannot be erased.)

1º memory – cannot be taken out from the system.

2º memory – Easily dispatch from the system.
13. ROM:

Here, the BIOS program is stored.

ROM called Non-volatile (It can keep the content even without a power source.

3 types of ROM used in PC:
(i.)
PROM (PROGRAMMABLE READ ONLY MEMORY)
Special type of programming device used to store programs in PROM chip.
Can read but doesn’t write.
One time programmable memory.
(ii.)
EPROM(ERASABLE PROM)
* Reusable
(iii.)
EEPROM (ELECTRICALLY ERASABLE PROM)

Using electricity, we can able to erase the program.

Program re-writed, this technique called as FLASING (or) FLASH PROM.
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14. CMOS:

Non – volatile RAM.

It cannot be erased.
15. RAM

SRAM

DRAM
MEMORY & IT’S TYPES
 Memory – organized into locations.
 Each memory location is known as one memory word.
 The no of bits in each location is known as “word length” of the memory.
 Word size of memory is 8 bits, 16 bits (or) 32 bits.
MEMORY CAPACITY:
The total number of locations in a memory is defined as the “memory capacity”.
MEMORY TYPES:
 Older computers use magnetic core memory, while the present day ones use semiconductor memory.
 The core memory – non-volatile
Semi-conductor memory – volatile
TYPES OF SEMI-CONDUCTOR:
Static memory (SRAM)
Dynamic memory (DRAM)
Static Memory:
 It preserves the contents of all the locations as long as the power supply is present.
Dynamic Memory:
 Dynamic memory can retain the content of any location only for a few milli-seconds.
RAM & ROM:
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(i.)
Read Write Memory (RWM)
(ii.)
Read Only Memory (ROM)
 Both RWM & ROM are RAM’s
RAM – Volatile
ROM – Non-volatile
When the power is switched off, RAM contents are lost but the ROM contents remain.
ROM TYPES:
ROM: READ ONLY MEMORY
 Memory that can only be read, but cannot be rewritten.
 Permanent memory, Non-volatile memory.
 Long term process program, where the data’s must be held permanently.
 BIOS is stored on ROM because the user cannot disrupt the information.
PROM: PROGRAMMABLE READ ONLY MEMORY
 This is basically a blank ROM chip that can be written, but only once (or)
programmed.
 It is much like a CD-R drive that burns the data into the CD.
 A user buys a blank PROM and enters the desired contents using a PROM
programmer (PROM burner)
 It can be programmed only once and yet cannot be erased.
EPROM: ERASABLE PROM
 It is just like PROM but you can erase the ROM by shining a special Ultra violet light.
 Doing this, wipes the data out, allowing it to be rewritten.
EEPROM: ELECTRICALLY ERASABLE PROM
 Also called “flash BIOS”
 This ROM can be re-written through a special software program.
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RAM:
 Volatile memory , means that data is lost when the power is turned OFF.
 RAM is used for temporary storage of program data.
SRAM:(Refreshing not required)
 Very fast.
 More expensive than DRAM
 SRAM, often used as cache memory due to its speed.
 This RAM will maintain the data as long as power is provided to the memory chips.
DRAM:
 For every 2 milliseconds, we have to refresh DRAM.
 Re-written in order to maintain its data.
 Cheap, small.
 This is done by placing the memory on a refresh circuit that re-writes the data several
hundred times per second.
Async SRAM
Sync SRAM
FPM DRAM (Fast page Mode)
EDO DRAM (Extended Data Out)
Burst EDO DRAM (BEDODRAM)
Sync DRAM (SDRAM)
RAM bus DRAM (RDRAM)
DDR-SDRAM
DDR-SDRAM 2
FLASH MEMORY:
 The name flash memory indicates that the erasing of a part of the memory cells take
place like a ‘FLASH’,
 Flash memory is used in the following equipments:
(i.)
Digital mobile phones
(ii.)
Digital camera
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(iii.)
MP3 music players
(iv.)
Handheld PC’S
(v.)
USB reader.
CACHE MEMORY:
USES:
(i.)
Execute the program very fast.
(ii.)
When the instruction is used frequently, we need cache memory.
(iii.)
Using cache, performance will be good.
TYPES:
1. Internal Cache
2. External cache
Internal Cache : Primary memory cache
 It is placed inside the CPU chip.
External cache : Secondary memory cache.
 Located in motherboard.
 Asynchronous cache : It is very slow
 Synchronous cache : Very faster compared to Asynchronous cache.
MEMORY:
 Any device used for storing data is said to be “memory”.

1º memory – cannot be taken out from the system.

2º memory – Easily dispatch from the system.
3 types of ROM used in PC:
(i.)
PROM (PROGRAMMABLE READ ONLY MEMORY)
Special type of programming device used to store programs in PROM chip.
Can read but doesn’t write.
One time programmable memory.
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(ii.)
EPROM(ERASABLE PROM)
* Reusable
(iii.)
EEPROM (ELECTRICALLY ERASABLE PROM)

Using electricity, we can able to erase the program.

Program re-writed, this technique called as FLASING (or) FLASH PROM.
RAM:
 Very faster when compared to others.
 When a large amount of data to be stored, we use RAM.
SRAM:
 Refreshing not required.
 Speed is high compared to DRAM.
 Expensive
DRAM:
 For every 2 milliseconds, we have to refresh RAM.
 Less memory capacity needed to store data’s.
 Less Expensive
MASS STORAGE:
The earliest storage devices were punched paper cards, which were used as early as
1804 to control silk-weaving looms. Modern mass storage devices include all types of disk
drives and tape drives. Mass storage is distinct from memory, which refers to temporary
storage areas within the computer. Unlike main memory, mass storage devices retain data
even when the computer is turned off.
The main types of mass storage are:
Floppy disks: Relatively slow and have a small capacity, but they are portable, inexpensive,
and universal. A soft magnetic disk. It is called floppy because it flops if you wave it (at least,
the 5¼-inch variety does). Unlike most hard disks, floppy disks (often called floppies or
diskettes) are portable, because you can remove them from a disk drive. Disk drives for
floppy disks are called floppy drives. Floppy disks are slower to access than hard disks and
have less storage capacity, but they are much less expensive. And most importantly, they are
portable.
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Fig., Parts of floppy disk
Floppies come in three basic sizes:

8-inch

5¼-inch

3½-inch
Hard disks: Very fast and with more capacity than floppy disks, but also more expensive.
Some hard disk systems are portable (removable cartridges), but most are not.
It is a magnetic disk on which you can store computer data. The term hard is used to
distinguish it from a soft, or floppy, disk. Hard disks hold more data and are faster than
floppy disks. A hard disk, for example, can store anywhere from 10 to more than 100
gigabytes, whereas most floppies have a maximum storage capacity of 1.4 megabytes.
A single hard disk usually consists of several platters. Each platter requires two read/write
heads, one for each side. All the read/write heads are attached to a single access arm so that
they cannot move independently. Each platter has the same number of tracks, and a track
location that cuts across all platters is called a cylinder. For example, a typical 84 megabyte
hard disk for a PC might have two platters (four sides) and 1,053 cylinders.
In general, hard disks are less portable than floppies, although it is possible to buy removable
hard disks.
Optical disks: Unlike floppy and hard disks, which use electromagnetism to encode data,
optical disk systems use a laser to read and write data. Optical disks have very large storage
capacity, but they are not as fast as hard disks. In addition, the inexpensive optical disk drives
are read-only. Read/write varieties are expensive.
A storage medium from which data is read and to which it is written by lasers. Optical disks
can store much more data -- up to 6 gigabytes (6 billion bytes) -- than most portable magnetic
media, such as floppies. There are three basic types of optical disks:

CD-ROM: Like audio CDs, CD-ROMs come with data already encoded onto them.
The data is permanent and can be read any number of times, but CD-ROMs cannot
be modified.
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
WORM: Stands for write-once, read -many. With a WORM disk drive, you can
write data onto a WORM disk, but only once. After that, the WORM disk behaves
just like a CD-ROM.

Erasable: Optical disks that can be erased and loaded with new data, just like
magnetic disks. These are often referred to as EO (erasable optical) disks.
These three technologies are not compatible with one another; each requires a different type
of disk drive and disk. Even within one category, there are many competing formats,
although CD-ROMs are relatively standardized.
Tapes: Relatively inexpensive and can have very large storage capacities, but they do not
permit random access of data.
Mass storage is measured in kilobytes (1,024 bytes), megabytes (1,024 kilobytes), gigabytes
(1,024 megabytes) and terabytes (1,024 gigabytes).
Mass storage is sometimes called auxiliary storage.
I/O INTERFACES STANDARDS:
a) Keyboard Interface
Key board is serial data.

If we press a key, the keyboard send a scan code for the key by data.(i.e., bit by bit)

SIPO is used to convert serial bit into parallel bit to form 1 byte.

After forming byte, it sends IRQ1 to CPU by interrupt controller.

KB logic receives then scan by PPI(port A)

Again the PPI converts the scan code into.
b) Printer Controller

It is a parallel interface.

The interface between printer and controller is centronic.

Printer controller supports 2 modes
1) Programmed mode
2) Interrupt mode
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
Recent form of PC is LPT1, LPT2, and LPT3.
I/O Read
Address
bus
Data strobe
Reset
Auto
linefeed
Command
register
I/O write
Bi
directional
data buffer
Data
bus
Data register
Data
Error
Paper end
busy
Data ACK
Status register
Interrupt IRQ 7
Fig, Printer controller
c). CRT Controller

CGA supports both text and graphics mode and display or color CRT monitor

Video buffer acts as memory between CRT and CPU.

CPU is used to store text and graphics in video buffer.

CRT monitor retrieves the text and graphics.

We get dot pattern from ROM.

We can send video signal to monitor along with the signals HSYNC and VSYNC.
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SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
d). Floppy Disk Drive (FDD) Controller
I/O Read
NEC 765
FDC
Support
circuits
I/O Write
Address
bus
Drives
for
outgoing
signals
Write data
Select data
Motor ON
Select head
Bidirectional
buffer
Step other ctrl
signals
Data bus
Clock generator
Receiver
for
incoming
signals
Read data
Track 0
Write protect
index
Other status
signals
Fig, Floppy Disk Controller
FDC is connected to the SMPS bus and DMA controller.

Data transfer is done in DMA mode.

NEC 765 FDC is a programmable IC, is used to convert parallel to serial and serial to
parallel.

It is also used to generate the CRC characteristic.

FDC is used to control the FDD at different speeds.

The BIOS is used to supply the command to the FDC.

FDC supplies the control signal to the IC to IDC.

For each command, the set of commands is supplied to

FDC IC has a set of registers to store command.

ISR is used to read the command from the FDCIC.

Apart from FDC IC the additional circuits are
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SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
1) Address decoder
- It enables FDC
2) Control post
- To supply control signals over FDCIC and FDD.
3) Data separator
-used to separate data and clock pulse.
f). Hard Disk Controller

This is a block diagram of HDC.

Similar to FDC
Sector Buffer:
Used to store the data during read and write operation. During write operation
read the data from memory in DFA port and store in sector buffer.

HDC takes data from sector buffer and converts into serial data.

HDC adds clock pulses into the data and send MFM (Modified Frequency
Modulation) write data.

During RD operation MFM contains data and pulses.

HDC is used to separate data pulses and clock pulses. It should be
converted into parallel data and stored in sector buffer. finally it is stored
in memory(DFA mode)
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SUBJECT: COMPUTER HARDWARE AND TROUBLESHOOTING UNIT-1
fig., Hard disk controller
Error checking and correction logic:

It is used to generate 32 bit pattern.

Used to check whether an error is occurred or not.
Retry logic:

Used to retry operation even error is encountered.
Diagnostic logic:

Used to detect the malfunctions occurred in hard disk drive.
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